Organic light emitting diode display

ABSTRACT

An organic light emitting diode (OLED) display includes a substrate where OLEDs are formed and an encapsulation member fixed onto the substrate while covering the OLEDs. The encapsulation member includes a photochromic material so that the encapsulation member is colored by external light.

CLAIM OF PRIORITY

This application makes reference to, incorporates into thisspecification the entire contents of, and claims all benefit accruingunder 35 U.S.C. §119 from an application earlier filed in the KoreanIntellectual Patent Office on Dec. 23, 2008 and there duly assignedSerial No. 10-2008-0132374.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic light emitting diode (OLED)display. More particularly, the present invention relates to an OLEDdisplay having improved visibility outdoors by minimizing reflection ofexternal light.

2. Description of the Related Art

In an organic light emitting diode (OLED) display, display quality isgreatly influenced by external light. That is, when external light istransmitted to the OLED display, reflection of the external light occursin layers that form an organic emission element and a thin filmtransistor. For example, a metal layer used as an electrode has highlight reflectivity so that the metal layer reflects most of the externallight. The reflected external light is mixed with the light emitted froman organic emission layer such that visibility of the screen isundesirably deteriorated.

In order to solve the above-stated problem, a linear polarization filmand a λ/4 phase delay film are disposed in a side where the externallight is transmitted in a contemporary OLED display. In this structure,a polarizing axis is changed by 90 degrees when the external lightpasses through the linear polarization film and the λ/4 phase delay filmand is then reflected by internal layers, and therefore the externallight is absorbed since the external light cannot pass through thelinear polarization film. Through this theory, the reflection of theexternal light can be suppressed to thereby enhance visibility.

In the above-described structure, however, half of the light(non-polarized light) emitted from the organic emission layer is blockedsince the light cannot pass through the linear polarization film. Such alight loss undesirably decreases efficiency (luminance/powerconsumption) of the OLED display.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide animproved an organic light emitting diode (OLED) display.

It is another object to provide an organic light emitting diode (OLED)display having an advantage of enhancing visibility by minimizingreflection of external

light while maintaining high efficiency.

These and other objects may be attained in the practice of theprinciples of the present invention, with an OLED display constructedwith a substrate where OLEDs are formed and an encapsulation member thatis fixed onto the substrate while covering the OLEDs. The encapsulationmember includes a photochromic material so that the encapsulation memberis colored by external light.

The substrate may be a semiconductor substrate, and the encapsulationmember may be an encapsulation substrate. The encapsulation substratemay be formed of glass. The OLED display may further include aphotosensor disposed in an overlapped area of the semiconductorsubstrate and the encapsulation substrate.

The encapsulation member may be a thin film encapsulation layercomprising a plurality of inorganic layers and a plurality of organiclayers that are alternately stacked. The farthermost layer among theplurality of inorganic layers and the plurality of organic layers fromthe substrate may include the photochromic material. The OLED displaymay further include a photosensor disposed between the thin filmencapsulation layer and the substrate.

The photochromic material may include one selected from a group ofsilver halide, zinc halide, cadmium halide, copper halide, and magnesiumhalide.

The photochromic material may include one selected from a group ofspiropyrane, spironaphthoxazine dye, diarylethene derivatives,dehydropyridine, furylfulgide derivatives, and azobenzene derivatives.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention, and many of the attendantadvantages thereof, will be readily apparent as the same becomes betterunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings in which likereference symbols indicate the same or similar components, wherein:

FIG. 1 is an oblique view of an organic light emitting diode (OLED)display constructed as a first exemplary embodiment according to theprinciples of the present invention;

FIG. 2 is a cross-sectional view of the OLED display constructed as thefirst exemplary embodiment according to the principles of the presentinvention;

FIG. 3 shows a sub-pixel circuit of a panel assembly of FIG. 1;

FIG. 4 and FIG. 5 are partial cross-sectional views of the panelassembly of FIG. 1;

FIG. 6 is an oblique view of an OLED display constructed as a secondexemplary embodiment according to the principles of the presentinvention;

FIG. 7 is a block diagram of the OLED display according to the secondexemplary embodiment of the present invention;

FIG. 8 is a partial enlarged cross-sectional view of an OLED displayconstructed as a third exemplary embodiment according to the principlesof the present invention; and

FIG. 9 is a cross-sectional view of an OLED display constructed as afourth exemplary embodiment according to the principles of the presentinvention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention will be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown.

As those skilled in the art would realize, the described embodiments maybe modified in various different ways, all without departing from thespirit or scope of the present invention.

FIG. 1 and FIG. 2 respectively show an oblique view and across-sectional view of an organic light emitting diode (OLED) displayconstructed as a first exemplary embodiment according to the principlesof the present invention.

Referring to FIG. 1 and FIG. 2, an OLED display 101 according to thefirst exemplary embodiment includes a panel assembly 12 having a displayarea A10 and a pad area A20 and displaying a predetermined video andvisual image in display area A10, a flexible circuit board 14 fixed topad area A20, and a printed circuit board 16 electrically connected topanel assembly 12 through flexible circuit board 14.

Panel assembly 12 includes a first substrate (or, a semiconductorsubstrate) 18 and a second substrate (or, an encapsulation substrate) 22that is smaller than first substrate 18 and having an edge fixed tofirst substrate 18 by a sealant 20 (refer to FIG. 2). Display area A10is located in an area where first substrate 18 and

second substrate 20 are overlapped at an interior side of sealant 20,and pad area A20 is located on first substrate 18 at an external side ofsealant 20.

A plurality of subpixels are disposed in a matrix pattern in displayregion A10 of first substrate 18, and a scan driver (not shown) and adata driver (not

shown) are located between display area A10 and sealant 20 or at theexternal side of sealant 20 for driving the subpixels. In pad area A20of first substrate 18, pad electrodes (not shown) for transmittingelectrical signals to the scan and data drivers are located.

An integrated circuit chip 24 is mounted on pad area A20 of firstsubstrate 18, and flexible circuit board 14 is electrically connected tothe pad electrodes and integrated circuit chip 24. A protective layer 26is formed around integrated circuit chip 24 and flexible circuit board14 to cover the pad electrodes formed in pad area A20 for protection. Inflexible circuit board 16, electronic components are provided forprocessing driving signals, and a connector 28 is provided fortransmitting external signals to flexible circuit board 16.

In a rear side of panel assembly 12, a bezel (not shown) for increasingbending strength of panel assembly 12 or a buffering tape (not shown)for increasing impact resistance of panel assembly 12 may be formed.Flexible circuit board 14 fixed to pad area A20 is bent to the rear sideof panel assembly 12 to make flexible circuit board 16 face the rearside of panel assembly 12.

FIG. 3 shows a structure of a sub-pixel of the panel assembly of FIG. 1,

and FIG. 4 is a partial enlarged cross-sectional view of the panelassembly of FIG. 1.

Referring to FIG. 3 and FIG. 4, a sub-pixel of panel assembly 12 isformed of an OLED L1 and a driving circuit unit. OLED L1 includes ananode (hole injection electrode) 30, an organic emission layer 32, and acathode (electron injection electrode) 34, and the driving circuit unitincludes at least two thin film transistors T1

and T2 and at least one storage capacitor C1. The two thin filmtransistors T1 and T2 are a switching transistor T1 and a drivingtransistor T2, respectively.

Switching transistor T1 is connected to a scan line SL1 and a data lineDL1, and transmits a data voltage input to data line DL1 according to aswitching voltage that is input to scan line SL1 to driving transistorT2. Storage capacitor C1 is connected to switching transistor T1 andpower source line VDD, and stores a voltage that corresponds to avoltage difference between a voltage transmitted from switchingtransistor T1 and a voltage supplied to power source line VDD.

Driving transistor T2 is connected to power source line VDD and storagecapacitor C1, and supplies an output current I_(OLED) that isproportional to the square of the difference between the voltage storedin storage capacitor C1 and a threshold voltage to OLED L1. OLED L1emits light by output current I_(OLED). Driving transistor T2 includes asource electrode 36, a drain electrode 38, and a gate electrode 40, andanode 30 of OLED L1 may be connected to drain electrode 38 of drivingtransistor T2. The configuration of the sub-pixel is not limitedthereto, and may be variously modified.

In OLED L1, anode 30 is formed of a metal layer having a lightreflection characteristic, and cathode 34 is formed of a transparentconductive layer. Therefore, light emitted from organic emission layer32 passes through cathode 34 and second substrate 22 and is emitted out.Anode 30 reflects the light emitted toward first substrate 18 along withthe light emitted from organic emission layer 32 to second substrate 22to thereby enhance luminous efficiency. Second substrate 22 is an

encapsulation member that covers OLEDs L1 for protection, and is made ofglass.

In the first exemplary embodiment, a substrate on which external lightis incident, that is, second substrate 22, includes a photochromicmaterial which is an ultraviolet (UV) discoloration material. Secondsubstrate 22 including the photochromic material has a characteristicthat displays a color when UV light illuminates second substrate 22 andreturns to a transparent state when the UV light does not illuminatessecond substrate 22. The photochromic material is mixed with glassduring a manufacturing process of second substrate 22 and uniformlydispersed inside second substrate 22. In FIG. 4, photochromic material42 is schematically illustrated as round particles.

Any well-known photochromic material can be used as photochromicmaterial 42. For example, photochromic material 42 may be selected froma group consisting of silver halide, zinc halide, cadmium halide, copperhalide, and magnesium halide. Alternatively, photochromic material 42may be selected from a group consisting of spiropyrane,spironaphthoxazine dye, diarylethene derivatives, dehydropyridine,furylfulgide derivatives, and azobenzene derivatives. Photochromicmaterial 42 included in second substrate 22 is not, however, limitedthereto.

As described, second substrate 22 including photochromic material 42 hashigh light transmittance because second substrate 22 becomes colorlessupon exposure to weak sunlight, for example in a normal indoorenvironment. In addition, under a strong sunlight condition, secondsubstrate 22 becomes colored by photochromic material 42 and absorbsexternal light. That is, in the case that an

electron device using OLED display 101 is observed outdoors during thedaytime, second substrate 22 becomes colored (refer to FIG. 5).

Therefore, OLED display 101 according to the first exemplary embodimentof the principles of the present invention can increase visibility ofthe screen by reducing reflection of external light under a strongsunlight condition. In this case, transmittance of light emitted fromorganic emission layer 32 is reduced due to coloration of secondsubstrate 22, but the amount of the reduced transmittance of light isless than that in a case in which a linear polarization film and a λ/4phase delay film are applied, instead of the photochromic material, onOLEDs L1. Accordingly, efficiency (luminance/power consumption) of OLEDdisplay 101 can be improved.

FIG. 6 is an oblique view of an OLED display constructed a secondexemplary embodiment according to the principles of the presentinvention.

Referring to FIG. 6, an OLED display 102 according to the secondexemplary embodiment is the same as the OLED display of the firstexemplary embodiment, except that a photosensor 44 is formed inside apanel assembly 12. Like reference numerals are used for like elements ofthe first exemplary embodiment.

Photosensor 44 is disposed on a portion of first substrate 18 whichoverlaps second substrate 22. Photosensor 44 may be disposed betweensub-pixels in display area A10, or may be disposed between display areaA10 and a sealant 20 (refer to FIG. 2). FIG. 6 illustrates a case inwhich photosensor 44 is exemplarily disposed at an external side ofdisplay area A10. Photosensor 44 detects the amount of light passingthrough second substrate 22 in order to increase the light emissionintensity of organic emission layer 32 (refer to FIG. 4) when secondsubstrate 22 is colored.

FIG. 7 is a block diagram of the OLED display according to the secondexemplary embodiment of the principles of the present invention.Referring to FIG. 7, OLED display 102 includes photosensor 44, an analogto digital (A/D) converter 46, a data driver 48, and a panel assembly 12where display area A10 is formed.

Photosensor 44 is formed of various types of sensors that can detect theamount of surrounding light. For example, photosensor 44 may be formedof one of a photodiode, a charge-coupled element, a charge injectionelement, a photomultiplier tube, a spectroradiometer, and acomplementary metal-oxide semi-conductor (CMOS) photoelectric element.Photosensor 44 outputs a voltage signal or a current signalcorresponding to the amount of light passing through second substrate22. In this case, a coloration degree of second substrate 22 isincreased as the strength of the external light is increased, andphotosensor 44 can detect a small amount of external light.

A/D converter 46 receives a voltage or a current output from photosensor44 as an analog signal and converts the analog signal into a digitalsignal. By using the digital signal provided from A/D converter 46, datadriver 48 provides a data voltage that appropriately corresponds to thecoloration degree of second substrate 22 to panel assembly 12. The datavoltage output from data driver 48 is formed of individual data voltagesrepresenting red, green, and blue. For this, data driver 48 includes agamma controller 50.

Gamma controller 50 includes a plurality of gamma curves thatrespectively correspond to the coloration degree of second substrate 22,detected by photosensor 44. Data driver 48 can control the data voltageprovide to panel assembly 12 by using a data voltage setting valuestored in gamma controller 50.

By the above-described configuration, OLED display 102 according to thesecond exemplary embodiment can enhance visibility and contrast ratio ofthe display by increasing light emission intensity of organic emissionlayer 30 (refer to FIG. 4) as the coloration degree of second substrate22 is increased.

FIG. 8 is a partial enlarged cross-sectional view of an OLED displayconstructed as a third exemplary embodiment according to the principleof the present invention.

Referring to FIG. 8, an OLED display 103 according to the thirdexemplary embodiment is the same as the OLED display of the firstexemplary embodiment except that a thin film encapsulation layer 52 isprovided as an encapsulation member instead of the second substrate ofthe first exemplary embodiment. Like reference numerals are used forlike elements of the first exemplary embodiment.

Thin film encapsulation layer 52 is formed or two or more inorganiclayers 521 and two or more organic layers 522. Inorganic layers 521 andorganic layers 522 are alternately stacked. FIG. 8 illustrates a case inwhich thin film encapsulation layer 52 is formed by alternately stackingeach of two inorganic layers 521 and each of two organic layers 522.

Inorganic layer 521 may be formed of aluminum oxide or silicon oxide,and organic layer 522 may be formed of any one of epoxy, acrylate, andurethane acrylate. Inorganic layer 521 suppresses penetration ofexternal moisture and oxygen, and organic layer 522 eases internalstress of inorganic layer 521 or fills micro-cracks and pinholes ofinorganic layer 521.

Among the plurality of layers that form thin film encapsulation layer52, at least one layer includes a photochromic material 42 so that thinfilm encapsulation layer 52 is colored by external light. When at leastone inorganic layer 521 includes photochromic material 42, photochromicmaterial 42 is mixed with an inorganic layer forming material during theinorganic layer forming process so that photochromic material 42 can beuniformly dispersed inside inorganic layer 521. When at least oneorganic layer 522 includes photochromic material 42, photochromicmaterial 42 is mixed with an organic layer forming material during theorganic layer forming process so that photochromic material 42 can beuniformly dispersed inside organic layer 522.

The uppermost layer (the farthermost layer from first substrate 18)among the plurality of layers forming thin film encapsulation layer 52may include photochromic material 42. In this case, reflection ofexternal light by the layers forming encapsulation layer 52 can beminimized. FIG. 8 illustrates a case in which photochromic material 42is included in the uppermost organic layer 522 of thin filmencapsulation layer 522.

FIG. 9 is a cross-sectional view of an OLED display constructed as afourth exemplary embodiment according to the principles of the presentinvention.

Referring to FIG. 9, an OLED display 104 according to the fourthexemplary embodiment is the same as the OLED display of the thirdexemplary embodiment except that a photosensor 44 is provided in a lowerportion of a thin film encapsulation layer 52. Like reference numeralsare used for like elements of the first exemplary embodiment.

Photosensor 44 is disposed on a portion of a first substrate 18 which

overlaps thin film encapsulation layer 52. Photosensor 44 may bedisposed between sub-pixels in a display area A10, or may be disposed atan external side of display area A10. FIG. 9 illustrates a case in whichphotosensor 44 is exemplarily disposed at the external side of displayarea A10.

Photosensor 44 detects the amount of light passing through thin filmencapsulation layer 52 in order to increase light emission intensity ofan organic emission layer 32 (refer to FIG. 8) when thin filmencapsulation layer 52 is colored. Photosensor 44 is connected to an A/Dconverter and a data driver, and configurations and functions ofphotosensor 44, the A/D converter, the data driver, and a gammacontroller are the same as those of the OLED display of the secondexemplary embodiment.

While this invention has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. An organic light emitting diode (OLED) display, comprising: asubstrate where OLEDs are formed; and an encapsulation member that isfixed onto the substrate while covering the OLEDs, wherein theencapsulation member includes a photochromic material so that theencapsulation member is colored by external light.
 2. The OLED displayof claim 1, wherein the substrate is a semiconductor substrate, and theencapsulation member is an encapsulation substrate.
 3. The OLED displayof claim 2, wherein the encapsulation substrate is formed of glass. 4.The OLED display of claim 2, further comprising a photosensor disposedin an overlapped area of the semiconductor substrate and theencapsulation substrate.
 5. The OLED display of claim 1, wherein theencapsulation member is a thin film encapsulation layer comprising aplurality of inorganic layers and a plurality of organic layers that arealternately stacked.
 6. The OLED display of claim 5, wherein at leastone of the plurality of inorganic layers and the plurality of organiclayers comprises the photochromic material.
 7. The OLED display of claim5, wherein the farthermost layer among the plurality of inorganic layersand the plurality of organic layers from the substrate includes thephotochromic material.
 8. The OLED display of claim 5, wherein theinorganic layer is formed of one selected from a group of aluminum oxideor silicon oxide, and the organic layer is formed of one selected from agroup of epoxy, acrylate, and urethane acrylate.
 9. The OLED display ofclaim 5, further comprising a photosensor disposed between the thin filmencapsulation layer and the substrate.
 10. The OLED display of claim 1,wherein the photochromic material comprises one selected from a group ofsilver halide, zinc halide, cadmium halide, copper halide, and magnesiumhalide.
 11. The OLED display of claim 1, wherein the photochromicmaterial comprises one selected from a group of spiropyrane,spironaphthoxazine dye, diarylethene derivatives, dehydropyridine,furylfulgide derivatives, and azobenzene derivatives.
 12. The OLEDdisplay of claim 1, further comprising a photosensor disposed in an areawhere the substrate and the encapsulation member are overlapped.
 13. TheOLED display of claim 12, further comprising: an analog to digital (A/D)converter receiving an analog signal output from the photosensor, andconverting the analog signal into a digital signal; a data driverreceiving the digital signal output from the analog to digitalconverter, and providing a data voltage that corresponds to a colorationdegree of the encapsulation member.
 14. The OLED display of claim 13,wherein the data driver further comprises a gamma controller.